Mine roof bolt and bolting system



Aug. 2, 1960 E. J. HOHOS ET AL MINE ROOF BOLT lAND BOLTING SYSTEM Filed Nov. 22, 1957 2 Sheets-Sheet l INVENTORS. EDWARD J. HoHosnd 'Jn/m55 A Pref/ 720- BY WWW @WQ MMM/ Aug. 2, 1960 E. J. HoHos ETAL MINE ROOF BOLT AND BOLTING SYSTEM 2 Sheets-Sheet-2 Filed Nov. 22, 1957 INVENTORS. ow/wn J. Hof/ogni 1 Jamas A. ,QIC/fafa.

A BY/N gu,

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Y Y 2,947,279 MINE Roon` BOLT AND BoLTING SYSTEM y Edward J. Holros, Pittsburgh, and James AL Richard,

Monroeville,` Pa., assignors t'o Mine Safety Appliances Company, a corporation of Pennsylvania Filed Nov. 422, 195'17, Ser. No. 698,280

1 Claim. (Cl. 1116-414) inserted in holes that have been drilled up into the roof and the upper ends of the bolts then are expanded in some manner to anchor them in place. The bolts are tightened up to bolt the various strata of the roof together States atet into a strong beam. Nevertheless, in time the strata may start to separate and develop a load on the bolts. If the load becomes great enough, the bolts will stretch and fail without warning, thereby allowing the roof to co1- lapse. It would be highly desirable to have as early warning ofthe dangerous condition of a roof as possible.

It is among the objects of this invention to provide a mine roof bolting system, which will give clear warning if the roof starts to weaken, which permits the use of bolts that are all made the same initially, and which does not change the customary method of installing the bolts.

=In accordance with this invention, after the usual holes have been drilled in a mine roof, standard roof bolts are inserted in most of them and tightened in place to'hold the roof. At intervals, however, an indicating bolt is used. Such a bolt is weaker than the standard bolts so that it will break before the others in case the roof starts to sag. The lower end of the broken bolt then will fall4 and show by its presence on the iloor of the mine passage that the roof is dangerous. The indicating bolt may be made weaker than the standard bolts in various ways,d such vas by using a w'eaker material or by reducing the cross sectional area of the bolt at a given point.

The invention is illustrated in the accompanying drawings, in which Fig. l is a fragmentary cross section through a mine passage -and roof showing standard bolts and a broken indicating bolt;

Fig. 2 is a side view of another type of -indicating bolt in place in a mine roof; and

Figs. 3, 4 and 5 are fragmentary side views of further modiiied bolts.

Referring to Fig. 1 of the drawings, a mine roof 1 is bolted together at suitable intervals by standard roof bolts Z of any desired construction. Each of those shown extends up into a hole 3 that was drilled up into the roof. The upper end of the bolt is threaded into a Wedge shape nut 4. The lower end of the bolt has a head 5 that supports a heavy metal plate 6 which engages the roof. When the head is rst turned, the nut is pulled down into a split sleeve 7 provided with teeth that engage the side of the hole just tightly enough to keep it from turning with the bolt. This spreads the sleeve and pushes the teeth into the surrounding wall so that the head of the bolt will push the plate up tightly vagainst the roof. Other ways of anchoring the bolt in the roof can be used. The anchoring means form no part of this invention.

At intervals along and across the mine roof an indicat- 2 ing or warning bolt is substituted fora :standard bolt. For example, there may be one indicating bolt` among every ten standard bolts.- The indicating bolt 9 shown in Fig.V l looks the same asV the other bolts as far as size and shape is concerned, and it may be held in place in the same way. However, the material ofthe shank isweaker than that of the standard bolts. This weakness can be imparted by heat treatment'or the like or by using a different material, such as aluminum, a lower grade steel or reinforced plastic. The indicatingbolt is not used for supporting the roof, but is merely tightened enough to press the metal plate 10 snugly against the roof. If the roos strata separate Yso that the roof begins 'to sag, the pressure against the plate on the indicating bolt will cause the weak bolt to break long before the standard bolts have reachedtheir yield point. The portion of the bolt beneath the break will then fall down to the mine door as shown, and its presence there will clearly warn the miners that the roof is in dangerous condition and may fall because the remaining bolts are under a greatly increased load. Action can then be taken to add more roof bolts or posts, or to abandon the area. The attention of the miners will be directed to the broken bolt more readily if the bolt has been brightly colored so that it can be seen more easily in the dimly lit passage. Such an indicating bolt does not require a special hole to receive it or a special tool for astening it in place. Aside from its color, it'may look like the standard bolts with which it is used.

In the modification shown in Fig. 2, a standard bolt which has been modified is used as an indicating bolt.

v Thus, the shank 12 of the bolt is provided with a lateral notch 13v that is most conveniently formed by means of a saw cut. The depth of the notch will determine the lcxadrthat will break the bolt. If desired, the bolt can be marked or color coded to indicate how much roof pressure Vit can stand. There i's no danger of twisting oit the shank while the bolt is being installed, because the bolt is turned only until the plate 14 on its head 15 or other enlargement firmly eng-ages the roof. lf the load on the plate reaches a predetermined value, due to sagging of the roof, the concentration of strain in the area of the shank beside the notch will cause the bolt to break at that poi-nt. The metal plate and the portion of the bolt beneath the notch will then fall to the floor of the mine to indicate that the roof is in dangerous condition.

lIn the embodiment shown in Fig. 3, the shank 17 of the bolt is provided with an annular cut 1S that leaves the upper and lower portions of the shank connected by only a small central portion of much less diameter. All

of the strain of a sagging roof on the plate 19 supported by the bolt will be concentrated in this reduced section of the shank and break the bolt before nearby standard bolts are broken.

In Fig. 4 a bolt 21 is shown which has been provided with .a hole 22 extending transversely through it. This again reduces the cross sectional area of the shank and thereby produces a weakened section where the bolt will break as the roof starts to sag.

Instead of removing metal to reduce the cross sectional area of the shank, a standard bolt may be weakened by stretching it in ya tension machine to a point just beyond its elastic limit but not, of course, to the point'of rupture. This stretching of the bolt will cause it to neck down as shown in Fig. 5. A predetermined amount of pressurev Pa'renredAug. z, 1960'- illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claim, the invention may be practiced otherwise than as specically illustrated and described.

We claim:

In a mine'V roof the combination with a plurality of standard roofY support bolts including an indicating bolt, a plurality of openings formed in said mine roof, said roof support bolts andY said indicating bolt havingmeans securing the inner end of each of said bolts in respective roof openings, said indicating bolt having a shank portion of smaller diameter than said roof opening, said shank havinga weakened portion intermediate its ends and an enlarged portionV at its outer end, a plate o-f larger dimensions than the transverse dimensions of said roof openings intermediate said outer end portions and said roof, whereby sagging of the roof will break the indif-k eating bolt before the other bolts and the lower end of the broken bolt will fall and thereby warn of the roof sagging.

References Cited in the tile of this patent UNITED STATES PATENTS 200,104 Stone Feb. 5, 1878 869,443 Lund Oct. 29; 1907 2,085,074 Boyles June 29, 1937 2,725,843 Koski Dec. 6, 1955 2,740,315 Gouverneur Apr.' 3', 1956 2,747,454 Bowersett May' 29, 1956 2,804,798 Brilmyer Sept. 3, 1957 FOREIGN PATENTS 1,119,434 France Apr. 3, 1956 748,969 Great Britain May 16, 1956 

